This invention relates to an automatic sheet-feeder and, more specifically, to an automatic sheet-feeder for feeding sheets from the lowermost of a pile of sheets (hereinafter called a stack) placed on a sheet-tray and for circularly returning the sheets to the sheet-tray.
Generally, in the case of making a plurality of copied sets of an original document of a plurality of original sheets such as manuscript paper or copied paper (hereinafter called sheets), the copying operation has so far been carried out in such a manner that, first, the first sheet is placed on an original platen and is then copied, and next, the second sheet is placed in place of the first sheet on the original platen and is then copied, thereafter the same operation follows, and then all of the sheets are placed one after another on the original platen and are then copied.
Meanwhile, the copies made from the first sheet are sorted one by one to separate positions, and the copies made from the second sheet are superposed one by one on the first copies. Thereafter, the same superposing operation follows, and all of the copies are superposed successively and in order, so that a plurality of copied sets of the plurality of documents may be made. Such a copying operation as mentioned above has been very troublesome and complicated for copying operators.
To solve the above-mentioned difficulties, an automatic sorting means, that is called a sorter, has been manufactured for automatically sorting copied sheets one by one. It has, however, been inevitable that such a sorter has required many spaces to sort a large number of copied documents (e.g. 20 to 30 or more) and it has also been troublesome to take out the sets of copied documents one by one from the respective sorted positions.
Accordingly, in recent years, there have been various proposals of such a means as those described in, for example, Japanese Patent Examined Publication No. 34416/1975, Japanese Utility Model O.P.I. Publication No. 55445/1976, Japanese Patent Examined Publication Nos. 27343/1980 and 37536/1981, and the like. The means of this kind have been designed to operate in the following manner: When an original document comprising a plurality of sheets is set in the firm of a stack, the first original sheet thereof is conveyed onto an original platen to make one copy only and is then returned to the original stack. Next, the second original sheet is conveyed onto the original platen to make one copy only and is then returned to the original stack, and so on. After all of the original sheets are copied, they are returned to the original stack, and the respective copies are made up into a single set of the copied documents. The same procedure is successively repeated so as to make up into a prescribed number of the copied documents.
With the means of this kind, however, the following requirements must be fully satisfied:
(1) Every sheet is to be separated and conveyed one after another.
The reason is that, should there be two or more sheets conveyed together, the corresponding copied sheets will be missing from some sets of copied documents.
(2) Every sheet separated from the stack is to be properly conveyed to a given position on an original platen.
The reason is that, should there be a sheet improperly positioned in place on the original platen, an improper copy, a partly missing copy, or a skewed copy will result.
(3) Each sheet is to be kept from crumbling, tearing, and the like.
This requirement is important particularly when there are no extra copies of the document to be copied.
(4) Each sheet already copied is to be properly returned to the original stack.
The reason is that, should there be any sheet improperly returned to the original stack, the preparations for the subsequent copying operation are hindered.
(5) Every procedure such as sheet conveyance, copying, returning the sheet to the stack position, is to be carried out without fail, regardless of the sizes and thickness of the sheets which are to be copied.
The reason is that there may be some instances where the sheets of a document are different in size and thickness from each other. More particularly, in relation to requirement (5), when using a conventional bottom feed and recirculating type automatic sheet-feeder such as that described in Japanese Patent Examined Publication No. 40338/1981, there is the possibility of causing a defective sheet because, when copied sheets are returned to the stack on the original sheet tray, the sheet can not be superposed in the required correct position, and then the selvages of the sheets returned to the stack cannot be aligned. Therefore, the lowermost sheet of the stack cannot be conveyed therefrom.
With the purpose of preventing the above-mentioned undesirable possibility, there is also known a method of truing up the selvages of sheets in which a tilted sheet-tray is provided so as to urge the sheets by their own weight against a stop fitted to the lower part of the tray.
Even with the above-mentioned fixed sheet tray, however, defective sheet feeds are still caused, because some sheets do not stop at the desired position due to differences in the sizes, weights, circulating speeds, etc. of the sheets, so that the selvages of the sheets are not aligned. Particularly with a high-speed copying machine, the above-mentioned defect is very often caused, because the circulating speeds of the sheets (and original documents) are accelerated. For the purpose of avoiding the above-mentioned defects, there has been devised a suction type conveyor belt. However, this device has a complicated mechanism and, in addition, is noisy.